This situation only seems odd if you use the mathematical definition of the word average... which means "adding up a set of numbers, dividing them by the quantity and calculating the result." Or the statistical definition or "being at the midpoint" or "being the most common number in a set" as in median or mode.
If you apply those definitions, then it seems bizarre that 86% of a group turn out to be "average or above."
But that isn't how Dpreveiew uses the term.
It's pretty evident that they are using "average" to mean "ordinary" or "mundane." In fact, they have told us this many times.
And further, they DO NOT test the entire universe of cameras released. Just the ones they find interesting, innovative, or news worthy.
Dpreview doesn't seem to waste a lot of effort testing bad cameras. They only seem to do this if it is news worthy. Like if Canon lays an egg.
If they wanted to test every camera made, assuming it was even possible, then you would be treated to dozens of reviews waring you about $89 Norcents, Sakars, Digigital Concepts, Vivitars and no-name generic cameras sold at mass retailers. But then you might have to wait three years to see a review for the Nikon D5000, rather than waiting two months.
Would anyone really want them to do that?
There are other sites that review a much wider range of cameras. Of course, their reviews are not as thorough, and some are nothing more than glorified press releases.
--
Marty
http://www.flickr.com/photos/marty4650/sets/72157606210120132/show/
http://marty4650.zenfolio.com/p82379129/slideshow#h275db7e6
Panasonic FZ30, LX2, TZ5
Olympus E-510, Zuiko 12-42mm, 40-150mm, 70-300mm, Hexanon 40mm, 50mm